Local or regional anesthesia consists of injecting an agent about the nerves thereby producing a loss of sensation in a region or regions of the body. An example of local or regional anesthesia is an epidural block given to women to ease the pain of childbirth.
Peripheral pain management procedures are continuous peripheral nerve blocks which can be categorized into two types depending on the area of the body where the block is introduced. In upper extremity blocks, the majority of the continuous peripheral nerve blocks performed are in the brachial plexus, i.e., the shoulder and neck regions. Such nerve blocks in the area of the brachial plexus include: interscalene block, supraclavicular block and axillary block.
In lower extremity blocks, the majority of the continuous nerve blocks performed are in the lumbar plexus and the celiac plexus, i.e., the hips and waist areas. Nerve blocks performed in the region of the lumbar plexus are: sciatic block, femoral block, lateral femoral block, obturator block, popliteal block, ankle block and lumbar sympathetic block. Nerve blocks performed in the area of the celiac plexus include: the celiac plexus block, which blocks the splanchnic nerve bundle.
Continuous epidural anesthesia is a technique used to relieve acute and chronic pain, in which an anesthesiologist introduces a conduction catheter via an epidural needle into the patient's epidural space between T10 and L4. The catheter is advanced and checked for “flashback” to indicate whether the distal end of the catheter is properly emplaced in the patient, the needle is removed, and anesthesia is administered. The anesthesia blocks nerve impulses from nerves in the T10 (thoracic vertebra number 10) through S5 (sacral vertebra number 5) region.
The most popular epidural catheter currently in use is a closed-end, non-reinforced catheter with three to five side ports. The preference for the closed end catheter with side ports is due to lowered incidences of inadequate analgesia, i.e., improved drug dispersion, and less need for catheter manipulation. However, a significant drawback to using this type of catheter is the lack of reinforcement that makes the catheter prone to collapsing and/or kink formation during use. Kink formation can make proper placement of the catheter difficult.
To avoid the problems of catheter collapse and kinking associated with closed-end catheters, many anesthesiologists prefer to use a reinforced catheter. Reinforcement may come from a variety of sources including the incorporation into the catheter of wire, polymers, metallic ribbons and the like. A major drawback limiting the use of reinforced catheters is that these catheters are open-ended, which may result in the reinforcement, i.e., the wire or metallic ribbon, becoming detached from inside the catheter and presenting a puncture hazard to the patient. Open-ended catheters were also found in at least one study to provide a less even distribution of analgesia than closed-end catheters (See: Epidural catheters for obstetrics. Terminal hole or lateral eye? Reg. Anesth. November-December; 19 (6):378-85, 1994).
A number of inventions have been directed to solving this problem. For example, U.S. Pat. No. 3,757,768 issued to Kline provides an example of a catheter with the helices of a reinforcing spring embedded into the inner wall. Although this catheter can resist collapse of the catheter wall, it may be prone to kink formation because the spring is part of the catheter and cannot relieve torsional stress accumulated from inserting and advancing the catheter into a patient.
U.S. Pat. No. 3,942,632 issued to Cook provides a catheter consisting of an inner core wrapped by a spiraling fiber glass reinforcement surrounded by an outer core. The layered nature of this construction may help prevent catheter wall collapse but may not permit the release of torsional stress and therefore may not make the catheter resistant to kink formation.
U.S. Pat. No. 5,004,456 issued to Botterbosch et al. provides a catheter with a relatively soft distal portion joined to a relatively stiff portion to help prevent catheter wall collapse. This catheter does not provide reinforcement at the distal portion where it may be needed and further does not make any provision for kink resistance.
U.S. Pat. No. 5,947,940 issued to Beisel provides a catheter that is reinforced with a coil made of plastic ribbons. The reinforcing coil is incorporated directly into the catheter's body by being layered between an inner and outer core. The reinforcing coil can be wound less tightly to allow fluid to flow out of side holes in the catheter wall to provide a more even distribution of anesthesia. Although this catheter can provide resistance to catheter wall collapse, the invention of Beisel does not provide for kink resistance because of its construction incorporating the reinforcing coil directly into the catheter. Beisel teaches at col. 4, lines 4-6, that, “(i)t is impossible to terminate the coil short of the side holes since the unsupported, thin polyurethane tube would then kink or collapse and occlude.”
In addition to the problems of collapsing and kinking, proper location of the tip of the catheter, and hence the dispensing portion of the catheter, can also be a problem. X-rays can be used to locate a catheter's position, assuming that the catheter has at least some radiopaque components. However, transporting a patient to an x-ray machine, or waiting for the delivery of a portable x-ray machine to the patient, can result in the delay of the delivery of needed medication.